Fingerprints have uniqueness and permanence because fingerprints are different among individuals and do not change in their lifetime. Thus, fingerprints have been widely used in the situations where identification of an individual is required. An optical device that captures a fingerprint by using a two-dimensional image sensor such as a Complementary Metal Oxide Semiconductor (CMOS) image sensor or the like is known as one of the devices for acquiring such a fingerprint.
Among the optical devices that capture a fingerprint by using an image sensor, a transmission type fingerprint input device has been focused on (see Patent Literature 1). In a transmission type fingerprint input device, a light from a light source is caused to enter a finger and is scattered therein, and a light exiting from the surface of the finger is utilized to capture an image of a fingerprint.